Idle problems

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Idle problems

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Idle problems - 7/10/2007 7:52:22 PM

lbelew

Posts: 54
Joined: 7/10/2007
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I've got a 1985 that varies its idle RPM from 550 to 750, in park and in drive. Car runs great above 750 rpm. New plugs, cap, rotor, and MAF sensor. Can't detect any vacuum leaks. I was told that the 1985 did not have a power or burn-off relay for the MAF sensor. Any ideas. Thanks.

Post #: 1

RE: Idle problems - 7/10/2007 8:00:28 PM

cwb

Posts: 1508
Joined: 5/13/2007
From: eastern NC
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Vacuum leak. 100% probability.

http://www.corvetteforums.com/m_37283/tm.htm

print it out, put it in the bathroom.

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RE: Idle problems - 7/10/2007 8:01:00 PM

Superdzzz

Posts: 343
Joined: 5/4/2006
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My C4 '87 runs at 500 in park or drive(foot on the brake). Not sure why your's varies...

Ask Mech259

he might know...

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Post #: 3

RE: Idle problems - 7/10/2007 8:17:59 PM

cwb

Posts: 1508
Joined: 5/13/2007
From: eastern NC
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quote:

ORIGINAL: lbelew

I've got a 1985 that varies its idle RPM from 550 to 750, in park and in drive. Car runs great above 750 rpm. New plugs, cap, rotor, and MAF sensor. Can't detect any vacuum leaks. I was told that the 1985 did not have a power or burn-off relay for the MAF sensor. Any ideas. Thanks.

The answer to your burn-off relay question is also in the article. Fifth post (p. 23). It won't matter for yours however; we already know whatcha' got there...

< Message edited by cwb -- 7/10/2007 8:25:31 PM >

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RE: Idle problems - 7/11/2007 6:33:37 AM

mech259

Posts: 1759
Joined: 1/22/2006
From: Lumberton, Texas
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Throttle plates probably need cleaning. When they get carboned up, it is difficult for the plates to seal in throttle bore and the ECM has trouble controlling idle.

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Post #: 5

RE: Idle problems - 7/11/2007 5:47:22 PM

lbelew

Posts: 54
Joined: 7/10/2007
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Thanks for all of the input. I guess I'll try cleaning the throttle plates next. I read the article and tried the propane with no luck of locating a vacuum leak. The car has 30300 miles on it and is like new except for my idle problem. I've set my idle at 700 rpm in park and the car purrs, but at 500 it surges to 700. What do you guys think of an EGR issue. I currently do not have any codes stored or a service light. By the way I also have a 2000 and a 1979 vette. Thanks.

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Post #: 6

RE: Idle problems - 7/11/2007 5:51:35 PM

lbelew

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Joined: 7/10/2007
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One more thing to note, this is a 1985 car that has had about 2000 miles put on it in the last ten years. Thanks.

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Post #: 7

RE: Idle problems - 7/12/2007 8:14:04 AM

cwb

Posts: 1508
Joined: 5/13/2007
From: eastern NC
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30K doesn't seem like enough distance for a vacuum leak to develop. I can't imagine carbon build-up either.

...or anything else failing, mechanical-wise. Rubber and other organic fiber compounds - vacuum hoses and gaskets, COULD fail, given the time period.

So I gotta' stick with an intake leak somewhere. Get back on this one tho'... I'd really like to know on this one.

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RE: Idle problems - 7/13/2007 6:20:44 AM

RRT vette

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Joined: 7/12/2007
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I agree with cleaning the throttle body and the IAC also. You can usually hear vac leaks....like a hissing sound.

Does it make a difference if the engine is cold or hot? Usually a vac leak will disappear once the ECM goes closed loop. A easy test to do if you have an ohm meter is to check the resistance of the injectors hot and cold.

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Post #: 9

RE: Idle problems - 7/13/2007 7:28:03 AM

bill

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Joined: 6/24/2006
Status: offline

the burn off relay is behind the breadbox check the fuel filter and like said above clean the plates

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Post #: 10